SURFACE RUNOFF & SUBSURFACE RUNOFF

Surface Runoff FlowSpecifically refers to the water leaving an area of drainage and flowing across the land surface to points of lower elevation.What occurs when rain is not absorbed by the ground on which it falls and so then flows downhill.

Flow process is developed in two phases:1. At the beginning of the shower, the infiltration capacity is generally superior to the rain intensity; water will be completely infiltrated. 2. When the runoff process exceeds the infiltration capacity water flows into another area of the watershed with a superior infiltration capacity.

Meteorological factors affecting runoff: Type of precipitation (rain, snow, sleet, etc.) Rainfall intensity Rainfall amount Rainfall duration Distribution of rainfall over the drainage basin Direction of storm movement Precipitation that occurred earlier and resulting soil moisture Other meteorological and climatic conditions that affect evapotranspiration, such as temperature, wind, relative humidity, and seasonPhysical characteristics affecting runoff: Land use Vegetation Soil type Drainage area Basin shape Elevation Topography, especially the slope of the land Drainage network patterns Ponds, lakes, reservoirs, sinks, etc. in the basin, which prevent or delay runoff from continuing downstreamEffects of surface runoff1. Surface runoff causes erosion of the earth's surfaceThere are four principal types of erosion: Splash erosionIs the result of mechanical collision of raindrops with the soil surface. Gully erosionIt occurs when runoff continue to enlarge rills. It can transport large amounts of eroded materials in a small period of time. Rill erosionOccurs when the power of runoff is strong enough to cut a well-defined channel. These channels can be as small as one centimeter wide or as large as several meters Sheet erosionIs the overland transport ofsedimentby runoff without a well-defined channel.

2. Environmental effects3. Agricultural issues4. Flooding